Optimization selection method of high temperature superconducting dc cable

Abstract

The application relates to an optimization selection method of a high-temperature superconducting direct-current cable, which records the change of a magnetic field under different winding angles in three-dimensional simulation by establishing an accurate three-dimensional superconducting cable model through COMSOL, records the change of the magnetic field of a superimposed different harmonic component current strip, and decomposes the magnetic induction intensity in parallel and vertical directions, so that the average value of the magnetic induction intensity under different conditions is compared with the unit value and the reference value, three-dimensional cable electromagnetic analysis under different conditions is carried out on the cable under different conditions, and the analysis speed and accuracy of the cable are effectively improved. Meanwhile, the application analyzes an anisotropy influencing factor, provides a basis for winding of superconducting strips, and explores the application value of the high-temperature superconducting direct-current cable.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature superconducting DC power transmission technology, and in particular, it relates to an optimized selection method for high-temperature superconducting DC cables. Background Technology

[0002] High-temperature superconducting direct current (HTC) cables offer a novel power transmission method for future power grid construction due to their advantages such as small footprint, light weight, large transmission capacity, and low transmission loss. The U.S. Electric Power Research Institute (EPI) has assessed the economics of HTC cables, finding that when the cost of superconducting tape falls below $50 / kA·m, their economic advantages over conventional DC transmission technologies are significant. With continued research into superconducting DC cables, superconducting DC transmission technology will inevitably advance, and the price of superconducting tape will gradually decrease. In future power grid construction, HTC cables are expected to become an important means of addressing the imbalance between power supply and demand.

[0003] Many countries worldwide have achieved significant research results in high-temperature superconducting AC cables and established numerous demonstration projects, with relatively mature technology. Compared to AC cables, high-temperature superconducting DC cables exhibit virtually no line loss. Furthermore, with the development of new energy sources, more and more researchers are focusing on the research and fabrication of high-temperature superconducting DC cables. However, in non-ideal DC transmission systems, AC ripple currents can occur during IGBT turn-on and turn-off. Additionally, when faults occur on either the DC or AC side of the DC system, such as short-circuit grounding faults or voltage dips, the current flowing through the high-temperature superconducting DC cable will contain harmonic components, causing the magnetic field of the tape to fluctuate over time. This affects the tape's critical current and may consequently impact the system's stable operation. Currently, there are no domestic solutions for the precise winding and optimized design of superconducting tapes in high-temperature superconducting DC cables. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and propose an optimized selection method for high-temperature superconducting DC cables. By using COMSOL to establish an accurate three-dimensional superconducting cable model, three-dimensional simulation analysis is performed on tapes with different winding angles and superimposed harmonic components to observe the spatial and temporal changes of the magnetic field. In the three-dimensional simulation, the changes of the magnetic field under different winding angles are analyzed, and the magnetic induction intensity is decomposed in parallel and perpendicular directions to analyze the influencing factors of anisotropy. This provides a basis for the winding of superconducting tapes and has the application value of exploring high-temperature superconducting DC cables.

[0005] The technical problem solved by this invention is achieved through the following technical solution:

[0006] An optimization method for selecting high-temperature superconducting DC cables includes the following steps:

[0007] Step 1: Set parameters for the high-temperature superconducting DC cable strip and perform three-dimensional modeling to obtain the three-dimensional magnetic induction intensity distribution on the outside of the high-temperature superconducting DC cable strip and the magnetic induction intensity distribution on the strip under steady state. At the same time, the magnetic induction intensity distribution of different cross sections is obtained.

[0008] Step 2: Superimpose the harmonic components of the corresponding parameters onto the current flowing through the tape in Step 1 to obtain the magnetic induction intensity distribution on the three-dimensional high-temperature superconducting DC cable tape at different times.

[0009] Step 3: Perform vector decomposition on the magnetic flux density distribution obtained in Step 1 and Step 2, and calculate the average magnetic flux density.

[0010] Step 4: Change the parameters set in Step 1, and repeat Step 1, Step 2 and Step 3 to obtain the average magnetic induction intensity on the strip surface under different parameters;

[0011] Step 5: Use per-unit values ​​to represent the average magnetic induction intensity on the strip surface under different parameters in Step 4;

[0012] Step 6: Analyze the relative magnitude of the critical current under different conditions by analyzing the variation law of the per-unit value in Step 5, and then analyze the stability of the strip.

[0013] Moreover, the parameters in step 1 include: the winding helix angle, the diameter of the helical strip, the number of superconducting strips with uniformly arranged single conductive layers, and the current flowing through each strip.

[0014] Moreover, the specific implementation method of the three-dimensional modeling in step 1 is as follows: draw the strip cross section in the xy plane using COMSOL, then sweep along the spiral, set the time-varying current flowing through the strip, calculate the magnetic induction intensity distribution on the outside of the three-dimensional high-temperature superconducting DC cable and the magnetic induction intensity distribution on the strip after the sweep is completed, and obtain the magnetic induction intensity distribution of different cross sections.

[0015] Moreover, the parameters in step 2 include amplitude and frequency.

[0016] Furthermore, the specific implementation method of step 3 is as follows: the magnetic induction intensity (B) at each point (x, y, z) on the cylinder is... x B y B z The magnetic flux density is decomposed into vectors along the directions parallel and perpendicular to the cylindrical surface, resulting in the magnetic flux density vector B of the parallel strip. / / The magnetic induction vector B perpendicular to the strip ⊥ for:

[0017]

[0018]

[0019] Moreover, the parameter in step 4 is the winding helix angle.

[0020] Moreover, the specific implementation method of step 6 is as follows: as the winding helix angle increases, the parallel component of the magnetic induction intensity on the surface of the superconducting tape fluctuates within the range of the reference value, and the degree of change is small. The reason is that the annular component of the current flowing through the superconducting tape generates an axial magnetic field, and the axial component of the current flowing through the superconducting tape generates a circumferential magnetic field. The magnetic fields on the inner and outer sides change in the same way. The combined effect of the two results in a small degree of change in the parallel component. The vertical component of the magnetic induction intensity on the surface of the superconducting layer decreases as the winding helix angle increases, and the decreasing trend is more obvious. As the external magnetic field of the superconducting tape increases, its critical current will decrease. Therefore, as the winding helix angle increases, the critical current also increases.

[0021] The advantages and positive effects of this invention are:

[0022] This invention utilizes COMSOL to establish a precise three-dimensional superconducting cable model. In the three-dimensional simulation, it records the changes in the magnetic field under different winding angles and the changes in the magnetic field of the tape with superimposed harmonic components. Furthermore, it decomposes the magnetic induction intensity into parallel and perpendicular directions. By comparing the per-unit values ​​of magnetic induction intensity under different conditions, it enables electromagnetic analysis of the superconducting cable under various circumstances, effectively improving the speed and accuracy of cable analysis. Simultaneously, this invention analyzes the influencing factors of anisotropy, providing a basis for the winding of superconducting tapes and exploring the application value of high-temperature superconducting DC cables. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a single energized spiral strip generating a magnetic field;

[0024] Figure 2 This invention provides a schematic diagram of the external magnetic induction intensity distribution of a simulated three-dimensional high-temperature superconducting DC cable.

[0025] Figure 3 This is a simulation diagram of the magnetic induction intensity distribution on the strip material of this invention;

[0026] Figure 4 This is a schematic diagram of the magnetic induction intensity cross section on the simulated strip of the present invention;

[0027] Figure 5 This is a simulation diagram of the magnetic induction intensity on the xy section of the strip in this invention;

[0028] Figure 6 This is a simulation diagram of the magnetic induction intensity on the yz section of the strip according to the present invention;

[0029] Figure 7This is a simulation diagram of the magnetic induction intensity of the strip material at time 0 with superimposed harmonic components, as presented in this invention.

[0030] Figure 8 This is a simulation diagram of the magnetic induction intensity of the strip material with superimposed harmonic components at 0.3s, as presented in this invention.

[0031] Figure 9 This is a simulation diagram of the magnetic induction intensity of the strip material with superimposed harmonic components at 0.6s.

[0032] Figure 10 This is a simulation diagram of the magnetic induction intensity of the strip material with superimposed harmonic components at 0.9s.

[0033] Figure 11 This is a vector decomposition diagram of the simulated magnetic flux density of this invention;

[0034] Figure 12 The graph shows the relationship between the per-unit value of the magnetic flux density component and the helix angle.

[0035] Figure 13 This is a graph showing the trend of magnetic flux density over time after the addition of harmonics. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to the accompanying drawings.

[0037] like Figure 1 As shown, in superconducting applications, the tape is often wound at a certain angle. In the past, for the sake of saving the amount of superconducting tape used, a smaller value was generally selected in the design of superconducting tape winding. However, when the helix angle of the superconducting cable is different, the direction of the current flowing through the superconducting tape will also change, and the magnetic field generated by the current will also have certain differences. The change in the external magnetic field leads to the change of the critical current of the superconducting tape, which will ultimately affect the current carrying capacity of the high-temperature superconducting DC cable. In addition, in non-ideal DC transmission systems, such as when IGBTs are turned on and off, AC ripple current will also appear in the DC system. Furthermore, when a fault occurs on the DC side or AC side of the DC system, such as short-circuit grounding faults, voltage drops, and other different types of faults, the current flowing through the high-temperature superconducting DC cable will also have harmonic components, causing the magnetic field of the tape to fluctuate over time, thus affecting the critical current of the tape, and potentially affecting the stable operation of the system. Since two-dimensional simulation cannot adequately illustrate the influence of the three-dimensional characteristic of the winding helix angle on the winding of superconducting tape, this invention will perform three-dimensional magnetic field modeling of high-temperature superconducting DC cables and conduct magnetic field analysis by superimposing different harmonic component currents.

[0038] Step 1: Set parameters for the high-temperature superconducting DC cable strip and perform three-dimensional modeling to obtain the three-dimensional magnetic induction intensity distribution on the outside of the high-temperature superconducting DC cable strip and the magnetic induction intensity distribution on the strip under steady state. At the same time, the magnetic induction intensity distribution of different cross sections is obtained.

[0039] The parameters include: a 20° helix angle, a 16mm diameter helical strip, six uniformly arranged superconducting strips in a single conductive layer, and a 50A current flowing through each strip. The specific implementation method for 3D modeling is as follows: The strip cross-section is drawn in the xy-plane using COMSOL, then swept along the helix, and the time-varying current flowing through the strip is set to calculate the current as shown below. Figure 2 , Figure 3 , Figure 4 , Figure 5 and Figure 6 The three-dimensional high-temperature superconducting DC cable shows the external magnetic induction intensity distribution and the magnetic induction intensity distribution on the tape, and the magnetic induction intensity distribution of different cross sections is obtained.

[0040] Step 2: Superimpose the harmonic components with corresponding parameters onto the current flowing through the strip in Step 1, and calculate as follows. Figure 7 , Figure 8 , Figure 9 and Figure 10 The magnetic induction intensity distribution on the three-dimensional high-temperature superconducting DC cable tape at times 0, 0.3s, 0.6s, and 0.9s is shown.

[0041] The parameters include a superimposed harmonic component amplitude of 5A and a period of 1s.

[0042] Step 3: Perform vector decomposition on the magnetic induction intensity distribution obtained in Step 1 and Step 2, and calculate the average value of the magnetic induction intensity.

[0043] The magnetic field surrounding a superconducting tape can be categorized into directions parallel and perpendicular to the tape. Different directions and magnitudes have varying effects on the critical current of the superconducting tape; this difference in the influence of direction on the critical current is called anisotropy. In the modeling process of step 1, the wide facet of the tape and the cylindrical surface can be considered parallel. The process of decomposing the magnetic induction intensity into parallel and perpendicular directions is as follows: Figure 11 As shown. The magnetic field strength (B) at each point (x, y, z) on the cylinder is... x B y B z The magnetic induction intensity vector B of the parallel strip is obtained by decomposing the vector along the directions parallel and perpendicular to the cylindrical surface. / / The magnetic induction vector B perpendicular to the strip ⊥ for:

[0044]

[0045]

[0046] The total magnetic flux density on the surface of the superconducting layer is mostly parallel, with a small portion being perpendicular.

[0047] Step 4: Change the winding helix angle set in Step 1, and repeat Step 1, Step 2 and Step 3. That is, after changing the winding helix angle of the strip, simulate the magnetic induction intensity on the surface of the superconducting strip again to obtain the average value of the magnetic induction intensity on the surface of the superconducting strip under different winding helix angles.

[0048] Step 5: To more clearly observe the trend of magnetic flux density variation, per-unit values ​​are used to represent the average magnetic flux density on the superconducting tape surface under different parameters in Step 4. When analyzing the winding helix angle, the baseline value is set as the average value at a winding helix angle of 10°. The trend of magnetic flux density variation is as follows: Figure 12 As shown, when superimposing harmonics, the reference value is set to the average value of the unsuperimposed harmonics. The trend of magnetic flux density change over time after superimposing harmonics is as follows. Figure 13 As shown.

[0049] Step 6: Analyze the relative magnitude of the critical current under different conditions by analyzing the variation law of the per-unit value in Step 5, and then analyze the stability of the strip.

[0050] according to Figure 12 It was found that as the winding helix angle increases, the parallel component of the magnetic induction intensity on the surface of the superconducting tape fluctuates within a range around the reference value, with a relatively small degree of change. This may be because the annular component of the current flowing through the superconducting tape generates an axial magnetic field, while the axial component of the current flowing through the superconducting tape generates a circumferential magnetic field, and the magnetic fields on both the inner and outer sides change in the same direction. The combined effect of these two factors results in a small degree of change in the parallel component. The vertical component of the magnetic induction intensity on the surface of the superconducting layer decreases with the increase of the winding helix angle, and the decreasing trend is quite obvious. As the external magnetic field of the superconducting tape increases, its critical current decreases. Therefore, as the winding helix angle increases, the critical current also increases.

[0051] according to Figure 13 It is found that, due to the superposition of harmonic components, the magnetic induction intensity on the surface of the superconducting tape changes with the harmonic period. The parallel and perpendicular components of the magnetic induction intensity on the surface of the superconducting tape are in the same direction as the harmonic change, and reach the peak value at around 0.3s. That is, the critical current appears to be at a minimum value at around 0.3s, which means that the stability of the superconducting tape is poor at this time, and this should be taken into consideration in the design.

[0052] It should be emphasized that the embodiments described in this invention are illustrative rather than limiting. Therefore, this invention includes, but is not limited to, the embodiments described in the specific implementation. Any other implementations derived by those skilled in the art based on the technical solutions of this invention are also within the scope of protection of this invention.

Claims

1. An optimized selection method for high-temperature superconducting DC cables, characterized in that: Includes the following steps: Step 1: Set parameters for the high-temperature superconducting DC cable strip and perform three-dimensional modeling to obtain the three-dimensional magnetic induction intensity distribution on the outside of the high-temperature superconducting DC cable strip and the magnetic induction intensity distribution on the strip under steady state. At the same time, the magnetic induction intensity distribution of different cross sections is obtained. The parameters include: the spiral angle, the diameter of the spiral strip, the number of superconducting strips with uniformly arranged single conductive layers, and the current flowing through each strip. The specific implementation method of 3D modeling is as follows: draw the strip cross section in the xy plane using COMSOL, then sweep along the spiral, set the time-varying current flowing through the strip, calculate the magnetic induction intensity distribution on the outside of the 3D high temperature superconducting DC cable and the magnetic induction intensity distribution on the strip after the sweep is completed, and obtain the magnetic induction intensity distribution of different cross sections at the same time. Step 2: Superimpose the harmonic components of the corresponding parameters onto the current flowing through the tape in Step 1 to obtain the magnetic induction intensity distribution on the three-dimensional high-temperature superconducting DC cable tape at different times. Step 3: Perform vector decomposition on the magnetic flux density distribution obtained in Step 1 and Step 2, and calculate the average magnetic flux density. Points on the cylinder magnetic induction intensity The magnetic flux density is decomposed into vectors along the directions parallel and perpendicular to the cylindrical surface. The resulting vectors of magnetic flux density are parallel to the strip. Magnetic induction vector perpendicular to the strip for: ； ； Step 4: Change the parameters set in Step 1, and repeat Step 1, Step 2 and Step 3 to obtain the average magnetic induction intensity on the strip surface under different parameters; The parameter is the winding helix angle; Step 5: Use per-unit values ​​to represent the average magnetic induction intensity on the strip surface under different parameters in Step 4; Step 6: Analyze the relative magnitude of the critical current under different conditions by observing the variation of the per-unit value in Step 5, and then analyze the stability of the strip.

2. The method for optimizing the selection of a high-temperature superconducting DC cable according to claim 1, characterized in that: The parameters in step 2 include amplitude and frequency.

3. The method for optimizing the selection of a high-temperature superconducting DC cable according to claim 1, characterized in that: The specific implementation method of step 6 is as follows: As the winding helix angle increases, the parallel component of the magnetic induction intensity on the surface of the superconducting tape fluctuates within the range of the reference value, and the degree of change is small. The reason is that the annular component of the current flowing through the superconducting tape generates an axial magnetic field, and the axial component of the current flowing through the superconducting tape generates a circumferential magnetic field. The magnetic fields on the inner and outer sides change in the same way. The combined effect of the two results in a small degree of change in the parallel component. The vertical component of the magnetic induction intensity on the surface of the superconducting layer decreases as the winding helix angle increases, and the decreasing trend is more obvious. As the external magnetic field of the superconducting tape increases, its critical current will decrease. Therefore, as the winding helix angle increases, the critical current also increases.

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